Problem: MySQL: "Access denied..."

[Peter Proft]

Good evening dear members of this list!
(please excuse my bad English!)

I don't know what to do with my imp-installation! Thoe following Message
appears:

Warning: Access denied for user: 'hordemgr@localhost' (Using password:
YES) in /usr/local/plesk/apache/vhosts/webmail/horde/phplib/db_mysql.inc
on line 73

Warning: Access denied for user: 'hordemgr@localhost' (Using password:
YES) in /usr/local/plesk/apache/vhosts/webmail/horde/phplib/db_mysql.inc
on line 73

Warning: Access denied for user: 'hordemgr@localhost' (Using password:
YES) in /usr/local/plesk/apache/vhosts/webmail/horde/phplib/db_mysql.inc
on line 73

Yes, I read the other postings and changed the password and the rights
and tested the mysql-php-connection), BUT nothing lead to success.

Can anyone help me?

Peter Proft